In power tools, such as a router, an internal motor has a rotating shaft. The shaft is coupled to a chuck for receiving a cutting tool at the exposed end. Cutting tools of varying characteristics are selectively installed in, or removed from, the chuck depending on the job being performed by the user.
Conventional high-speed power tools such as routers often employ collet-type chucks attached to the shaft of the power tool. Such collet-type chucks have flexible jaws which may be opened or closed through the use of a rotary nut. The disadvantage with such a chuck mechanism is that the shaft of the router, onto which the collet is coupled, must be held stationary while the rotary nut is loosened or tightened.
There are generally two types of prior art collet-type chucks used. The first requires the user to use two wrenches, one to hold the shaft stationary while the other is used to turn the rotary nut. For a general description of a router utilizing such a chuck, and its use, the reader is referred to The Art of Woodworking Portable Power Tools, at 69-73 (Time-Life Books 1992). In the second alternative, the power tool includes a locking device which will lock the shaft in place when it is desired to change cutting tools by loosening and tightening the rotary nut. An example of a router using a shaft locking device is disclosed in U.S. Pat. No. 5,191,968 which issued on Mar. 9, 1993 to McCurry.
A disadvantage inherent in the conventional chucks described is the requirement that the shaft of the tool be locked before the cutting tool can be changed. Attempts have been made in the past to develop a chuck which would eliminate the need to lock the shaft of the driving apparatus in order to change cutting tools. However, in many cases, these prior art chucks do not adequately secure the cutting tool to the driving apparatus. This is especially true when such chucks are used in conjunction with high-speed power tools, such as modern day routers, which typically operate at speeds up to 25,000 rpm. Also, many of these prior art chucks require the user to apply a great amount of force in order to secure the cutting tool in the chuck. Furthermore, such prior art chucks are oftentimes complex in design and expensive to manufacture. Finally, none of these chucks suggest the mechanism disclosed and claimed in this specification, nor do they provide the same advantages. A couple of those patents are briefly reviewed here to show the state of the art.
U.S. Pat. No. 2,676,809 issued on Jun. 18, 1953 to Smith discloses a "Tool Holder Bushing." The mechanism disclosed incorporates two identical metal halves which are held together by a pair of spring rings to form a bushing which is then placed in a drill chuck. after a cutting tool shank is inserted into the bushing, a set screw threaded through the wall of the drill chuck forces the two halves of the bushing together, thereby clamping the cutting tool.
U.S. Pat. No. 5,096,212 issued on Mar. 17, 1992 to Walsh discloses a "Chuck For Power Tools." The mechanism disclosed includes a first tool bore into which a collet or a cutting tool shank is inserted and a second bore intersecting that first tool bore. Within the second bore are two clamping elements which may be drawn together into a clamping relationship upon the collet into which a cutting tool shank has been inserted, or upon the cutting tool shank directly, thereby securing the cutting tool shank within the chuck.
None of these prior art chucks employ a device which is not only easy to manufacture, but capable of securely retaining the shank of a cutting tool easily and without the exertion of undue force. More specifically, none of these prior art patents disclose a camming mechanism or any other mechanism designed to use leverage to increase the clamping forces upon the collet or cutting tool shank. Accordingly, there remains a need for a simple mechanism by which cutting tools may be easily, quickly and securely retained within a chuck.